The invention concerns a mechanical device which converts the wind energy into rotational mechanical energy; consisting of a cross-wind-axis rotor structure, having multiple orientable aerodynamic surfaces or blades around its periphery, mounted parallel to the rotor axis; each of these blades being interconnected with another orientable aerodynamic surface or stabilizer, mounted on the same radial line as the blade, at a smaller radius and parallel to the blade, so that, as the rotor revolves by the action of the wind, said blade and said stabilizer are able to pivot simultaneously and essentially parallel to each other around their respective pivot axes, in the course of aligning themselves, into a pitch angle, where the opposing pitching moments created by the aerodynamic lift forces over said blade and said stabilizer, equilibrate each other, and where the aerodynamic lift forces are the optimum to induce the necessary torque to spin up the rotor.
Cross-wind-axis wind turbines with orientable blades, are predicted to have power coefficients greater than for any other wind turbine exceeding the theoretical maximum of 0.593 of propeller type wind-axis wind turbines, due to the fact, that the rotor projected area into the wind is crossed two times by each blade during one revolution, duplicating the effective working area and decelerating a larger portion of the wind than does a propeller type wind-axis wind turbine of the same projected area of rotor disk.
To fully achieve this prediction, the pitch angle of each blade, must be continuously changed during rotation according to the instantaneous peripheral angular position of the blade, to optimize the angle of attack between the chord of the airfoil-shaped cross section of the blade and the changing incidence angle of the relative wind.
Additionally, the amplitude of this angular pitch variation must vary with the celerity or "tip speed ratio" .lambda., (which is the relationship between the peripheral tangential speed of the blade V.sub.tB, divided by the wind speed V.sub.0), in order to comply with the amplitude variation of the blade relative wind incidence angle .PHI.B with said celerity.
This difficult task is a job worth doing, when the following additional advantages of the cross-wind-axis wind turbines over the propeller type wind turbines are taken into account:
a) Fixed Cross-wind rotor axis:
A cross-wind-axis rotor mounted vertically on top of a tower, eliminates the requirement of aligning the rotor axis with the wind, since it can accept the wind from any direction; this characteristic permits the rotor to extract the energy of a given wind or gust instantaneously regardless of any rapid changes in wind direction.
Considering that the energy available from the wind is proportional to the cube of the velocity, the feature of not having to take time to head the machine into the wind provides additional energy extraction capability over that of a propeller type wind turbine.
This rotor disposition also eliminates the troublesome gyroscopic vibration, which is the consequence, of the natural resistance of any rotating mass against the directional change of its spinning axis.
The expense of the rotor supporting turntable and of the orientation driving mechanism, together with the automatic controls are also saved, and by eliminating these elements, a more integral and reliable unit is achieved.
The vertical drive shaft can be prolonged to ground level, where all the necessary equipment can be easily installed at a more convenient reach for maintenance purposes. The vertical cross-wind-axis rotor also eliminates the problem of ensuring the continuity of the generator electrical cables, from the movable generator to ground level.
b) Straight blades:
It is obvious that a straight blade is easier to calculate and fabricate than a twisted propeller type blade. Being supported usually, at two intermediate points, the straight blade of a cross-wind-axis rotor, is more rigidly supported than a propeller type blade with pivoting capability supported at one end.
A cross-wind-axis wind turbine with orientable blades, is known as Cyclogyro, or Cycloturbine, in which the control of the blade pitch angle is accomplished by means of a central cam mechanism, which must be oriented into the wind.
Because of the fixed geometry of the governing cam, the control of the amplitude of the blade pitch angle variation with the celerity, is not accomplished, therefore the acceleration performance of the Cyclogyro is poor, but even though, a high peak power coefficient of 0.60 is expected; which is not yet the optimum.
The complexity of the orientable central cam mechanism and of the long rods which transmit the movement to the blades, are factors to be considered in the evaluation of this turbine.
Another cross-wind-axis wind turbine with orientable blades, known as Gyromill, has been tested by the McDonell Douglas Aircraft Corporation, in which the control of the blade pitch angle is achieved by means of electronic sensors and servomechanisms. The technical sophistication of this turbine plays against its initial cost and its reliability.
The invention, aims to maximize the great energy production capability of cross-wind-axis wind turbines, by totally matching the pitch angle control of each individual blade, with an extremely simple method, that is to install an additional orientable aerodynamic surface or stabilizer, mechanically linked to each blade, so dimensioned and positioned, that, as the rotor revolves, the aerodynamic lift forces created by the relative wind over the blade and the stabilizer, will produce opposing pitching moments about their respective pivot axis, and as result of their mechanical interconnection, both surfaces will pivot simultaneously and essentially parallel to each other, into an optimum pitch angle, where said opposing pitching moments equilibrate each other.
The pitch angular positioning of each blade and of its respective stabilizer, occurs instantaneously, assuring a perfect coupling and synchronization to the changing direction of the actuating relative wind, at any celerity.
The tangential components of the lift forces created by the relative wind over the blade and the stabilizer, have the same direction, so that, their combined action will induce an added positive torque to spin up the rotor.
The invention expected real peak power coefficient of 0.70, represents a 50% increase in comparison to the real peak power coefficient of a propeller type wind turbine and 16% increase above the peak power coefficient of the Cyclogyro. This advantage added to the mechanical simplicity of the invention, constitutes a real breakthrough, which will make more feasible the wide use of the wind energy.
Further advantages of the invention will become apparent from a consideration of the drawings and ensuing description thereof.
One way of carrying out the invention is described below with reference to drawings which illustrate in detail one specific prefered embodiment. Additional drawings describe in general other suitable embodiments of the invention.